Player creates the story?

I don't know how to identify games like Elegy for a Dead World which is pretty much a non-game where player just fills in text prompts for a story, and includes a mode where player provides All text of the story.

This same concept essentially also describes Sleep Is Death but there's no writing in similar manner.

I was also looking for a suitable tag for Elegy for a Dead World, but couldn't find one. So I suppose a new tag needs to be created as you suggested.

It's not any form of emergent storytelling, since that's when it's Not prompted or included in the game itself.

Maybe I'm missing something but I don't see what would be the problem with a tag player-created story or similar like you suggested.

I felt it was missing something, or could be somehow understood to fit in cases where it shouldn't, though honestly I haven't been able to think any such instances (but that usually happens much later when such errors start cropping up).

Add Cant Drive This to this as of yet unnamed group.

It occurs to me that these games have User Generated Content and use a Live Editor to make it. Thus: ugc-liveeditor

UGC tag was mostly for the ability to Share the content with the masses, so it wouldn't be as suitable for this since not all of these have that (Elegy for a Dead World does IIRC, Sleep is Death does not).

I would prefer playercreatedstory currently, though it needs to be distinguished from branching stories or similar clearly.

Well, Sleep of Death does include a live editor and the story is 'cooperatively' created live. Content can be created before the game starts but when it does start it's assembled and reassembled with story on-the-fly.

But I think I think see your point. Live story is one thing, live content is another?

They're better handled as separate concepts, yes. Though if there's sufficient need, a combined tag could be added for games that have both (such as if they are or become an actual genre of their own).